JP2010209605A - Piled-raft foundation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piled-raft foundation with superior earthquake resistance without improving a ground. <P>SOLUTION: In this piled-raft foundation 10, a structure 12 is constructed on a soft ground 16. The soft ground 16 is a soft viscous soil ground in a normal consolidation state or in a state near that state in which consolidation settlement is produced by the weight W of the structure. The soft ground 16 is not improved. The base of the structure 12 is a direct base 14, and first piles 22 are embedded just beneath the columns 28 of the structure 12. The first piles 22 are cast-in-place concrete piles, PHC piles, or steel tube piles, and have a length reaching a hard support ground 20, and the bottom ends of the piles are embedded into the support ground 20. Second piles 24 are embedded into the lower surfaces of the slabs and beams of the direct base 14. The second piles 24 are PHC piles or steel tube piles, and have a length reaching an excessively consolidated ground 18 with less consolidation settlement, and the bottom ends of the piles are embedded into the excessively consolidated ground 18. The length of the second piles 24 is shorter than that of the first piles 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piled raft foundation that supports a structure constructed on soft ground.

  Soft ground where excessive consolidation settlement occurs when the full load of the constructed structure is applied cannot support the structure directly on the foundation. For this reason, the pile foundation which supports a structure with the support pile which reaches to the support ground in the lower layer of soft ground is adopted. However, when the supporting ground is in a deep position, a long supporting pile is required, and there is a problem that the construction cost increases.

  Therefore, the adoption of piled raft foundations as a rational foundation form to replace pile foundations in soft ground is increasing. The piled raft foundation has a structure in which a friction pile is directly added to the foundation, and the structure is supported directly by the foundation, and the settlement of the structure is suppressed by the friction pile (Patent Document 1).

  As shown in FIG. 4, the piled raft foundation 80 of Patent Document 1 is obtained by improving the soft ground 16 having poor properties immediately below the structure 12 to a ground improvement foundation 82 having a large supporting force. The direct foundation 14 of the structure 12 is supported with a force P2). Further, the friction pile 84 does not reach the support ground 20, and is embedded in the overconsolidated ground 18 below the soft ground 16. Thereby, the foundation 14 is directly supported by the friction pile 84 (supporting force P1), and the settlement of the structure 12 is suppressed.

  The ground improvement foundation 82 is obtained by improving the soft ground 16 immediately below the structure 12 to a solidified state by, for example, a deep mixing treatment method, and can support the entire load of the structure 12 by design. It is like that.

  However, although the construction method of Patent Document 1 is generally an inexpensive construction method, when the scale of the structure is large, it is necessary to improve a large amount of ground over a large area, so it cannot be said that the construction method is inexpensive. . The ground improvement foundation 82 is insufficient in shear resistance against a horizontal load that acts during an earthquake.

Japanese Patent No. 3765000

  In view of the above facts, an object of the present invention is to provide a piled raft foundation excellent in earthquake resistance without improving the ground.

  The piled raft foundation according to the first aspect of the present invention is a piled raft foundation that supports a structure, and is provided on a soft ground and a first pile buried directly under a pillar of the structure. The first pile and the direct foundation supported by the soft ground, and the second pile that supports the direct foundation and is rooted in the overconsolidated ground under the soft ground. It is characterized by.

  According to invention of Claim 1, the 1st pile is embed | buried directly under the pillar of a structure, and the foundation is directly supported by the 1st pile and the soft ground. In addition, the second pile supports the foundation directly by rooting the tip into the overconsolidated ground.

  Thus, since the 2nd pile is supporting the foundation directly by rooting the tip part in the overconsolidated ground where the consolidation settlement is small, it is not necessary to improve the soft ground. As a result, the construction cost is reduced, and the construction cost can be further reduced by appropriately selecting the number of second piles to be used.

  Moreover, since the 1st pile and the 2nd pile resist both with respect to the horizontal load which generate | occur | produces at the time of an earthquake, the resistance force with respect to a horizontal load becomes high.

  According to a second aspect of the present invention, in the piled raft foundation according to the first aspect, the second pile intersects a bearing force fracture surface which is a slip surface of the soft ground.

According to invention of Claim 2, the 2nd pile is embed | buried so as to cross | intersect the bearing capacity destruction surface which is a slip surface of the soft ground which generate | occur | produces at the time of an earthquake.
Thereby, a 2nd pile acts so that the bearing capacity destruction surface at the time of an earthquake may be sewn, and generation | occurrence | production of the slip of a soft ground can be suppressed because a 2nd pile becomes an obstruction.

The invention according to claim 3 is the piled raft foundation according to claim 1 or 2, wherein the pile length of the first pile is longer than the pile length of the second pile, or the pile diameter of the first pile is the first pile. It is characterized by being larger than the pile diameter of 2 piles.
According to invention of Claim 3, the pile length of a 1st pile is made longer than the pile length of a 2nd pile, or the pile diameter of a 1st pile is made larger than the pile diameter of a 2nd pile.

  Thus, by making the pile length of the first pile longer than the second pile, the first pile can be embedded in a stronger ground located deeper than the overconsolidated ground, and consolidation settlement of the structure can be suppressed. . Moreover, the pile peripheral area of a 1st pile increases by making the pile diameter of a 1st pile larger than a 2nd pile, a big supporting force can be obtained from the surrounding ground, and the consolidation settlement of a structure can be suppressed.

  Since this invention is set as the said structure, it can provide the piled raft foundation excellent in earthquake resistance, without improving the ground.

It is a figure which shows the basic composition of the piled raft foundation of this invention. It is a figure which shows the supporting force when the horizontal load by an earthquake acts on the piled raft foundation of this invention. It is a figure which shows the supporting force when the eccentric load by an earthquake acts on the piled raft foundation of this invention. It is a figure which shows the basic composition of the piled raft foundation of a prior art example.

As shown in FIG. 1, in the piled raft foundation 10 according to the first embodiment, a structure 12 is built on a soft ground 16.
The soft ground 16 is a ground of soft viscous soil in a normal consolidated state in which excessive consolidation settlement occurs due to the weight W of the structure or a state close thereto. Despite the poor properties, the soft ground 16 directly under the foundation 14 has not been improved.

  The foundation of the structure 12 is a direct foundation 14 having a hollow portion, and the bottom surface of the direct foundation 14 is provided on the soft ground 16. The first pile 22 is embedded immediately below the pillar 28 of the structure 12, and the weight W of the structure 12 is transmitted to the first pile 22 via the pillar 28.

  The first pile 22 is a cast-in-place concrete pile, a PHC pile (high-strength prestressed concrete pile), or a steel pipe pile, and has a length that reaches the hard support ground 20 in the lower layer of the overconsolidated ground 18. It is embedded in the support ground 20.

  Moreover, the 2nd pile 24 is embedded in the bottom face of the direct foundation 14 in which the foundation slab and the foundation beam were provided. The second pile 24 is a PHC pile or a steel pipe pile, has a length that reaches the overconsolidated ground 18 with less consolidation settlement in the lower layer of the soft ground 16, and the lower end is embedded in the overconsolidated ground 18. . The length of the second pile 24 is shorter than that of the first pile 22.

  Thus, since the lower end part of the 1st pile 22 is rooted in the support ground 20, and the foundation 14 is supported directly (supporting force P3), the consolidation settlement of the structure 12 is suppressed. Moreover, the 2nd pile 24 roots a lower end part in the overconsolidated ground 18, and supports the foundation 14 directly (supporting force P4).

  As a result, it is not necessary to improve the soft ground 16 directly below the foundation 14, and the construction cost can be reduced. Moreover, compared with the case where all are supported by the 1st pile 22 (support pile), since the 2nd pile 24 is short, the freedom degree of design increases, and the support position of the 2nd pile 24 is set with the magnitude | size of load and the strength of a ground. Thus, the second pile 24 can be designed economically. Furthermore, since the burden on the foundation slab of the direct foundation 14 can be reduced and cost reduction by economical slab design can be expected, the overall construction cost can be reduced.

  Note that the pile length of the first pile 22 is longer than the pile length of the second pile 24. Thus, by making the pile length of the 1st pile 22 longer than the 2nd pile 24, the 1st pile 22 can be rooted in the firmer support ground 20 in the deeper position than the overconsolidated ground 18, and the structure 12 The consolidation settlement can be suppressed.

Next, the horizontal load at the time of an earthquake is demonstrated.
As shown in FIG. 2, the horizontal resistance H5 of the first pile 22 and the horizontal resistance P6 of the second pile 24 act on the horizontal load H received by the structure 12 during the earthquake. Resist the horizontal load H with both resistances.

  The first pile 22 is a cast-in-place concrete pile, a PHC pile, or a steel pipe pile, and the second pile 24 is a PHC pile or a steel pipe pile. For this reason, compared with the ground improvement made into the solidified state by the deep mixing process method etc., for example, the resistance with respect to a shear force is large. As a result, the resistance to the horizontal load H during an earthquake can be increased.

Next, the eccentric load at the time of an earthquake is demonstrated.
As shown in FIG. 3, for the eccentric load (diagonal load) M at the time of the earthquake, the vertical support force P7 of the first pile 22 and the vertical support force P8 of the second pile 24 are directly foundations, respectively. 14 to resist the eccentric load M of the structure 12 with both resistance forces.

  At this time, since the eccentric load M has different sizes depending on the distance from the center point of the deviation, the values of the vertical support force P7 of the first pile 22 and the vertical support force P8 of the second pile 24 are Different values depending on the location. The 1st pile 22 and the 2nd pile 24 are set as the dimension which can resist the largest eccentric load M assumed by both resistance force.

  Further, as shown in FIG. 3, when the eccentric load M is received, a so-called slip is generated in which the ground on the lower surface of the foundation 14 is pushed directly toward the side of the structure 12 in the surface layer of the soft ground 16. At this time, a boundary surface between the ground portion pushed out by the generated slip and the surrounding non-moving ground is referred to as a supporting force breaking surface and is indicated by a broken line 26.

  A plurality of second piles 24 are embedded inside the supporting force breaking surface 26 so as to intersect the supporting force breaking surface 26. Thus, the second pile 24 acts so as to sew the supporting force breaking surface, becomes an obstacle when the soft ground 16 slips, and resists the slip. Thereby, generation | occurrence | production of the slip of the lower surface of the foundation 14 directly can be suppressed.

  Furthermore, the vertical support force P7 of the first pile 22 and the vertical support force P8 of the second pile 24 act on the vertical load (not shown) due to rocking during the earthquake, and both Resist rocking with resistance. Thereby, locking of the structure 12 is suppressed.

  In addition, the 2nd pile 24 should just support the foundation 14 directly, and the pile head of the 2nd pile 24 does not need to be fixed to the foundation 14 directly. Thereby, it is hard to act on the 2nd pile 24, and damage to the junction part of the pile head of the foundation 14 and the 2nd pile 24 directly can be prevented.

  In the above description, the first pile 22 has a length to be embedded in the support ground 20, but the first pile 22 has a large diameter, the pile peripheral area of the first pile is increased, and a large supporting force is obtained from the surrounding ground. The structure to obtain may be sufficient. At this time, if the first pile 22 having a large diameter has a supporting force for suppressing the settlement of the structure 12, the length of the first pile 22 is shortened, and the lower end portion is not allowed to be embedded in the supporting ground 20 Also good.

DESCRIPTION OF SYMBOLS 10 Piled raft foundation 12 Structure 14 Direct foundation 16 Soft ground 18 Overconsolidated ground 20 Support ground 22 1st pile 24 2nd pile 26 Bearing surface failure surface (slip surface)
28 pillars

Claims (3)

It is a piled raft foundation that supports structures,
A first pile buried directly under the pillar of the structure;
A direct foundation provided on soft ground, supported by the first pile and the soft ground;
A second pile supporting the direct foundation and rooted in an overconsolidated ground under the soft ground;
Piled raft foundation with.   2. The piled raft foundation according to claim 1, wherein the second pile intersects a supporting force fracture surface that is a sliding surface of the soft ground.   The pile raft foundation according to claim 1 or 2, wherein a pile length of the first pile is longer than a pile length of the second pile, or a pile diameter of the first pile is larger than a pile diameter of the second pile.

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